The present invention relates to an automated automotive test system. In particular, the present invention provides input protection for an automated breakout box.
With the advent of integrated circuits, and with the increasing use of sophisticated electronic, electric and electromechanical sensors and control systems in automobiles, the testing and servicing of automobiles has presented ever-increasing challenges. At the present time, many tests of electrical systems, sensors and components of an automobile are made manually by a technician who unplugs a multipin connector between the vehicle's electronic control module (ECM) and the vehicle sensors and controls. The technician makes voltage and resistance measurements between various pins of the connector using a multimeter. The technician making those measurements is required to move the multimeter probe to the appropriate measurement points. It is also necessary to set the multimeter to the proper measuring formula, such as volts or ohms.
This manual testing procedure has many drawbacks. In particular, the technician must follow detailed instructions in order to perform the proper tests. The instructions require that the technician set the proper condition, select the proper test points, read the equipment properly, and compare the reading to the listed tolerances specified in the instructions.
Some test systems have been developed which simplify some of the test operations. These devices use selection switches to select the proper test points. While this helps to some extent, the technician is still required to use the instructions, set the multimeter, and compare readings to the listed tolerances for that measurement.
As the number of electrical systems and sensors increases, the number of possible combinations of points which need testing increases as well. An automated breakout box, therefore, would preferably make use of switching devices to make connections between the testing circuitry and the points to be tested. Analog multiplexers are available which are capable of selecting among a large number of different inputs or outputs.
Analog multiplexers have a maximum input which should not be exceeded. However, signals generated by internal combustion engines typically have a wide dynamic range that can exceed the maximum level which the multiplexer is able to switch. If this occurs, the multiplexer can be burned out.